Process of producing oligodynamic metal biocides



March 1, 1960 z, v, MOUDRY 2,927,052

PROCESS OF PRODUCING OLIGO DYNAMIC METAL BIOCIDES Filed March 20, 1953 INVENTOR ZDENEK V. MOUDRY,

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ATTORNEY5 PROCESS OF PRODUCING OLIGODYNAMIC METAL BIOCIDES Zdenek Vaclav Moudry, Northfield, 111., assignor to United States Movidyn Corporation, a corporation Illinois Application March 20, 1953, Serial No. 343,705

1 Claim. (Cl. 167-14) This invention relates to an improved process'for pro ducing oligodynamic metal microbicides and to. novel oligodynamic metal microbicides of increased efficiency.

The present application is a continuation-in-part of my copending application, Serial Number 174,781, filed July 19, 1950, now abandoned. I v

In general, the invention relates to the Iproductionof oligodynamic metal microbicides by the reduction of oligodynamic metal salts, through the action of actinic light, in such a manner as to produce a stable dispersion of essentially nonagglomerated microparticles of the elemental metal. By microparticles, I refer to particles which do not exceed a few hundred 'augstrom (A.U.) in mean dimension.

The term oligodynamic metal does not appear to have a clearly defined meaning in the art. Inthespecification and claim, I emplo'y thisterm to define. certain metals, namely, silver, copper, gold, antimony, arsenic, cadmium, cobalt, germanium, iridium, mercury, palladium, platinum, zinc, bismuth, rubidium, "tellurium and thallium, which in microparticulate form have the power units of producing oligodynamic death of. microorganisms. V

Oligodynamic death, to be distinguished from ordinary death or poisoning, refers to death. brought about by an amount of the active material which is so small that ordinary death or poisoning could not accountfor. the biological action.

A great amount of work has been done in thepastto produce oligodynamic materials which would becommercially satisfactory, but very little in the way of satisfactory results appears to have been accomplished. Lack minoid, etc.

of success in this art prior to my invention: appears to V have resulted from inability to obtain adequately high biological activity, and from the difliculty in producing a satisfactorily stable dispersion of the particulate oligodynamic material. The present invention'provides' an improved process by which satisfactorily stable oligodynamic dispersions are produced which have many times the biological eflicacy of oligodynamic' materials heretofore produced. To my knowledge, the invention provides for the first time a particulate: oligodynarnic metal product wherein the mean dimension of the measurable particles is less than 200 A.U., and, according to one embodiment of my invention, I am able tosproduce a product wherein the mean size of the measurable particles is below 75 AU. As will hereinafter appear,

I ascribe to such extremely small particle size a major sterilized but. also upon withdrawaliofithe solutionziand 2,927,052 .1 teased-Mea 1.

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. 2 subsequent, contact of the surface with a heavily can taminated material, this latter material is sterilized'by-tlie biological'action of -oligodynamic material remaining upon the treated surface. I have observed that such residual biological activity persists through many weeks and through many contacts with contaminated liquids. While I can give no conclusive explanation for the existence of such residual activity, it appears that this'phenomenon is dependent upon the existence in the oligo: dynamic product of extremely small particles, some of these particles being retained by a solid surface by, reason of adsorption and'mech'anicaltrapping; V A further unique advantage of the invention -lies in theproduction o'f oligodynamicv particles each containing at least two metals in elemental but physically, combinedform. As will appear in' detail hereinafter, the invention provides for the simultaneous reduction of aplurality of oligodynamic metal salts, or of one oligodynamic metal salt and the salt of 'a non-oligodynamic metal, in such manner that a material proportion "ofthe metal microparticles produced contain both metals in elemental form,

the. physical'configuration and behavior of such comf posite particles. conforming to the configuration and be havior of an alloy. I have observed that the use of a second metal salt, either oligodynamic or non-oligody; namic, results in production of microparticles of sub stantially smaller size and in a marked increase in the oligodynamic killing power of the product, which 'induewholly or inv part to thesmaller par adsorption, of the metal to'the surface of'the-micro organism, butsubsequent advances in colloidfscienceand physicalchemi'stryf; and in methods and equipment for measuringquantitative chemical processes-have 'leduto rejection of t his theoryJ It has alsobeen suggested that the action is catalytic, thatitjdependsupon the forma: tion of metal peroxides, or upon existence of an alubu- None of these theories appear to be maintainable today, and it isnow generally agreed that oligo dynamic killing power varies inversely as theparticle size or subdivision of the-oligodynamic metal. This pres ent theory can be substantiated by relating :the oli'gtv dynamic activity to solubility, which in turn. is related to particle size.

I have discovered that dispersions of .oligodynainic metal microparticles smaller than'2OO A.U. canzb'e pro; duced by preparing an aqueous solution of a water solitble salt of an oligodynamic metal containing a. certain 'mercially available gelatins is totally ineffectivev to"'-p1:o-'

ducestable .dispersions of imicroparticles of oligodynami'c' metal of the median size above referred. to. For my process to be'operable-to produce stable dispersions o'fi such. microparticles, the gelatin employed must have a the characteristics ofKnox Gelatin #841,.Emanufacturedl.

by the. Chas. B. Knox Gelatine. Co., Knox 'Bldg;, John's town, N.Y. Knox Gelatin #841 is a very clear,'mediun's jelly strength, acid .type gelatin-made from fresh frozen? pork skins by acid treatment and acid hydrolysis; Thisgelatin has :a-. gel strength. ofzl'25-f250; a viscosity of2tl"-' 4.0 millipoisesinr6 /a% aqueous solution:at""C.,' and apHIof 3-5.. in aqueous solution. This gelatin is very strongly positively charged in aqueous solution and jhas an isoelectricpoint of 1.8-8.3. The-cation content 1 very, low. Analysis of: KnoxiTGelatin #s4rzshows' air ash analysis of 3%, substantially all of the ash being calcium, with very minute non-measurable traces of silicon, aluminum, iron and phosphates. The calcium constituent of the gelatin is present as calcium collagenates. It appears that the ash analysis of .3% is probably a practical minimum for the natural product, and that the calcium ash analysis can be increased to at least about 1.2% This particular gelatin is manufactured from freshfrozen pork skins by acid treatment and acid hydrolysis. During hydrolysis the characteristics above referred to change progressively and the desired gelatin is withdrawn as a fraction when these characteristics have reached their proper values.

The only known equivalent of Knox Gelatin #841 is the ordinary gelatin of commerce in Germany and Czechoslovakia. This gelatin is prepared from the skins of bovine animals, has a pH of 5.8 in water and, upon analysis, shows 2.67% ash consisting substantially entirely of calcium.

The gelatin functions as a protective colloid, isolating the oligodynamic metal particles as they are formed and thus substantially preventing agglomeration of the particles. Particle size of the product appears to be in part a function of the reaction rate, and perhaps of other reaction conditions, and I have found that reduction by actinic irradiation will readily produce measurable particle sizes on the order of 100 A.U. and smaller when the salt is reduced in the presence of a gelatin having the characteristics of Knox Gelatin #841, but that microparticles of this extremely small size cannot be prepared when other gelatins are employed.

The gelatin employed must be free from ionizable halogen, else the particle size of the oligodynamic metal will be inordinately large.

The relative proportions of water-soluble oligodynamic metal salt and gelatin may vary widely. Thus, on the basis of 100 cc. water, the oligodynamic metal salt may be present as .01-90 parts by weight, and the gelatin as ".01-50 parts by weight.

an intensity of at least 45 milliwatts per square foot, that at least 40% of the total radiation must lie in the infrared portion of the spectrum, that at least 25% of the total radiation must lie in the ultraviolet portion of the spectrum, and that the ultraviolet portion of the radiation must include a material proportion of light emitted at 3130 A.U. and at 3660 A.U. If the intensity of the actinic light employed is materially less than 45 milliwatts per square foot, reduction will not proceed at a rate suflicient to give adequate elemental oligodynamic metal. As has been stated, it appears that the particle size of the product decreases as the rate of reduction increases, and it is accordingly desirable to maintain the irradiation at a high level of intensity so as to shorten the reaction time. It appears that the actinic light serves both to cause reduction and to break the reduced metal particles into particles of smaller size, and I have observed that if the intensity of the actinic light is materially below 45 milliwatts per square foot, the particle size of the product will be undesirably large. In general, the period of irradiation may be in the range of from a few seconds, when light of high intensity is employed, to about one hour when the intensity is decreased to about the minimum value just mentioned. It is desirable to make the intensity as high as possible, and I find that intensities on the order of 1000 milliwatts per square foot, attainable with presently available eq mnereial Ultraviolet lamps, are highly desirable.

In carrying out my process, I prefer to employ an apparatus of the type illustrated in Fig. l. The initial solution of the oligodynamic metal salt, containing Knox Gelatin #841, is placed in the mixing and storage tank 1. This solution flows, at a rate determined by flow gage 2, into a trough 3, hence downwardly across the sloping irradiation surface 4 into the trough 5 and thence to the receiver 6. All parts in contact with the liquid material may be of stainless steel. Positioned above the irradiation surface 4 is a reflector 7 carrying dependent radiation shields 8. A series of ultraviolet lamps 9 is arranged in progression along the line of flow of the solution, the lamps being supported in any suitable manner below the reflector 7. The solution flows by gravity in a thin film over the surface 4 and is irradiated by actinic light from the lamps 9 until entering the trough 5. The time of irradiation may thus be adjusted by changing the angle of the irradiation surface 4, and the material may of course be run through the apparatus as many times as desired. In commercial practice, I perfer to make the irradiation time on the order of a few seconds, with only one pass of the solution through the apparatus. The thickness of the liquid film may be on the order of 1 mm. or less.

The following examples are illustrative:

The silver nitrate is dissolved in a portion of the water, a suspension of the gelatin in the remaining water is then prepared, and the silver nitrate solution and gelatin suspension combined. The resulting mixture is then passed through an irradiating device such as that shown in Fig. l, the lamps being chosen to .provide an actinic light of the spectral characteristics hereinbefore described and an intensity of about 1,062 milliwatts per square foot, and the apparatus being so constructed that the liquid suspension is subjected to such irradiation for approximately 15 seconds.

The resulting product is a stable aqueous dispersion of silver microparticles, the measurable portion of the particles having a median maximum dimension of A.U.

This product was diluted with water to provide a dilution of 1:5,000,000 on a volume basis. For comparison, a control product was prepared by adding monomethyl-p-aminophenol sulphate as a reducing agent to an aqueous mixture of silver nitrate and gelatin, the median particle size of the resulting oligodynamic silver being approximately 400 A.U. The control product was diluted with water to a 125,000,000 dilution by volume. In each case, the water for dilution contained sufiicicnt Escherichia coli to provide 50,000 organisms per cc. of final liquid. The two diluted solutions were allowed to stand for 24 hours and the number of living organismswas then determined by standard techniques as recommended by the Department of Agriculture. No viable organisms were found by repeated tests in the product of this example, while many viable organisms were found in the control product.

Example II An aqueous suspension of silver nitrate was prepared in the same manner as explained in Example I, and the suspension was then passed through an irradiating apparatus of the type shown in Fig. 1, the irradiation period being 150 seconds, and the actinic light having the spectral characteristics hereinbefore described but an intensity of approximately milliwatts per square foot. The resulting product was a stable aqueous dispersion of silver microparticles, the measurable portion of the particle having a median maximum dimension of 100'A.U.

.;.I his,. product was diluted to 115,000,000 as in-Examplel, the diluted product containing 50,000 Escherichia coli organisms per cc. of final liquid. The diluted product so obtained was compared with a control product identical with the control product of Example I. The two diluted solutions were allowed to stand for 24 hours and the number of living organisms was then determined. No viable organisms were found by repeated tests in theproduct of the present example, while many viable organisms were found still to be present in the control product.

Example III An aqueous suspension of silver nitrate is prepared in the. same manner as explained in Example I, and the suspension then passed-through an'apparatus of the type shown in Fig. 1, the irradiation period being one hour and. the actinic light, having the spectral characteristics hereinbefore, described, and an intensity of 45 milliwatts' per square foot. The resulting product is a stable aqueous dispersion of silver microparticles, the measurable portion of the particles having a median maximum dimension less than 200 AU.

The. product was diluted tov 125,000,000 as in Examplel, the dilutedproduct containing 50,000 Escherichia coli organisms per' cc. of final liquid. After 24 hours, repeated tests showed no viable organisms present.

ILWill be noted that in the foregoing examples, the Silver, nitrate and Knox Gelatin #:841Qare present in a proportion of 12.3. On a purely empirical basis, this. proportion is desirable from the standpoint of cost, fiowability and oligodynamic metal content desirable for certain commercial purposes. The. proportion. of silver nitrate may be varied within the range of .01-90 parts by weight, and that of the gelatin within .01-50 parts by weight, based on 100 parts by weight water, without materially changing the particle size of the oligodynamic metal in the product.

While the examples are limited to silver nitrate for simplicity, the water soluble salt of any other oligodynamic metal, as herein defined, may be employed inthe same proportion of .01-90 parts by weight.

Composite or plural metal microparticles having a median maximum dimension less than 200 AU. can also be prepared in accordance with my invention- To accomplish this, I prepare an aqueous solution of a plu rality of water-soluble metal salts, at least one salt being. of an oligodynamic metal, the salts preferably having a..common non-metallic ion. The non-metallic ion can in no case be sulphate or sulphite. If silver isone of the metals, the non-metallic ions must not be halogen.

Iuzthissolution, I incorporate an ionizable-halogen-free gelatin having the characteristics of Knox Gelation #841. L. then irradiate the resulting suspension With actinic light, of the spectral characteristics and intensity hereinbefore. specified, for a period of from a few seconds. to about one hour, in order to simultaneously reduce the plural metal salts.

The total combined quantity of the metal salts may be within the range of .01-90 parts by weight, based on 100. parts by weight of water. The gelatin may be:presout as .Ol-SO parts by Weight on the same basis.

In addition to one salt of an oligodynamic metal, one or more salts of a non-oligodynamic metal having good alloy forming properties may be employed, such metals being aluminum, beryllium cerium, chromium, iron, lead, lithium, magnesium, manganese, molybdenum, nickel, rhodium, silicon, strontium, tantalum, tin, titanium, tungsten, vanadium and zirconium.

.When my invention is carried out in accordance with this, embodiment, starting with at leasttwo salts, the product contains a major proportion of .rnicroparticles, each of which contain the metal of each salt in. elemental ,physieallycombined form. As is the case when only one oligodynamic salt} is; emnleyedmhegmicroparticles of the product are substantially un-agglomerated, thehdis p'ersion is stable, andth'e measurable microparticlesgof oligodynamic metal range below 200v A.U. in the mean maximum dimension. However, I, find that :whenat least two salts are simultaneously reduced by actinic light in accordance with the invention, themean maximum di: mension of the micropaiticlestends to decrease, and

that products having a maximum measurable particle reaction in accordance with this embodiment of, the in vention results in the complete disappearance, from the solution, of the metal present in the lowest concentration.

The following examples are illustrativeof this embodie. ment of-theinvention:

Exampl'eJV Parts by Weight Distilled Water Silver. nitrate (reagent igrade)x 5 Cupric nitrate (reagent grade) 1'15 Knox Gelatin #841 2.3

The two salts are dissolved in a portion of the water, a suspension of the gelatin is made inthe remaining water, and the salt solution and gelatin suspension corn bined. The resulting mixture is then passed through-an irradiating apparatusv such as that shown in Fig. 1, the

lamps being chosen to. give an actinic light having the" spectral characteristics hereinbefore specified and'an in tensity of about 1,062 milliwatts per' square foot, the apparatus being so constructed that the liquid is subjected'to such irradiation forapproximately 15. seconds. The product is an aqueous dispersion of oligodynamic metal'microparticles, amajor proportion of the micro particles containing both silver and'copper in elemental but physically combined form, the mean longest dimension of the measurable microparticles being approxi= mately 20 A.U., and the largest dimension of the preponderance of the measurable microparticles Ibeing in'the range of 7.5 A.U. or less. Theparticles are essentially non-agglomerated and the dispersion is stable over. long periods of time; i i

The product-of Example IV was diluted to a concern tration of=j12100,000,000fon a volume basis, the,'water for dilution including sufficient Escherichia, bill to give- 50,O00 organisms per cc. of final liquid; 'fA- control product was prepared-by reducingan aqueous "solution of silver nitrate,'containing gelatin, with monomtethyl-p; aminophenol sulphate as a reducingfagent, the resulting product having a particle size of about 400 AU. The control product was diluted to. a concentration ofv 1:l00,000,000 in'thesame manneras the product of the present example, so that the dilutedco'nt'rol productfideluded the same concentration of Escherichia colt; Both" products were allowed to stand for a period of 24hour's and were then tested for living or'ganisms. Repeated tests showed no viable organismsin the product of the; present example, while many viable oranisms were found, to exist in, the control product.

Example V An aqueous suspension' fo'f Knox Gelatin #841, silver. nitrate and cupric nitrate, in. the same proportions as in Example IV, was prepared andir'radiated rinthemanner described. The intensity 0f the. actinic was.45

7 watts per square foot and the time of irradiation one hour.

The product is an aqueous dispersion of oligodynamic metal microparticles, a major proportion of the microparticles containing both silver and copper in elemental but physically combined form. The mean maximum dimension of the measurable particles is less than 200 A.U.

The oligodynamic killing power of the product of the present example was composed with that of a control product produced as described in Example IV, both products being diluted to a concentration of 1:l00,000,000 containing 50,000 Escherichia coli per cc. of the final liquid. After 24 hours, no viable organisms could be detected in the product of this example, while many viable organisms were detected in the control product.

While silver nitrate and cupric nitrate were employed in these examples for purposes of simplicity, equivalent products can be prepared by using salts of a plurality of the other oligodynamic metals, as defined herein, or by using one oligodynamic metal salt and one or more salts of the non-oligodynamic metals hereinbefore recited.

As in the case of use of a single oligodynamic metal salt, this embodiment of the invention also requires the use of both a gelatin having the characteristics of Knox Gelatin #841 and actinic light of the intensity and spectral characteristics hereinbefore specified, if a stable dispersion of oligodynamic microparticles smaller than 200 A.U. is to be obtained.

Throughout the specification, I have referred to the size of the measurable portion of the oligodynamic particles. Particle size of the products of the invention has been determined with great care by the use of electronmicrographs wherein the particles were magnified on the order of 40,000 times, so that a particle of l mu appears in the photograph as a 4 cm. image. The average maximum dimensions of the greatest number of like particles was taken as the mean particle size. On this basis, the mean particle size of the measurable particles of the products of all of the examples herein is less than 200 A.U., and that of Example IV is 20-75 A.U. Proceeding in accordance with Example I, the mean particle size of the measurable particles of the product will always be less than about 100 A.U., the size diminishing as the intensity of irradiation is increased so that the reduction time is shortened. When plural salts are employed, the particle size will be smaller in each case than for the -corresponding product produced from a single oligodynamic salt. I have observed that, in addition to the measurable particles in the product, the electronmicrographs indicate the existence of extremely small, unmeasurable particles which are thought to be particles of the oligodynamic metal. With existing methods and equipment, it appears to be impossible to determine with any reasonable accuracy either the chemical nature or the effect of this background material.

It will be noted that the invention produces stable dispersions of oligodynamic particles of extremely fine subdivision, and that the use of both the particular type of gelatin referred to and actinic light of the characteristics specified herein is necessary to obtain such a product. I have observed that, in addition to the question of particle size, stability is a most critical factor when dealing with oligodynamic materials. While it may be possible to produce oligodynamic products of fairly small particle size by the use of chemical reducing agents, I have found that products so produced are always characterized by lack of stability. Where a chemical reducing agent is employed, even in the presence of a gelatin having the characteristics of Knox Gelatin #841, the particles of oligodynamic metal in the product tend to agglomerate excessively, so that the effective particle size of theproduct increases with time.

Certain of the products of my invention, and particularly products prepared either from a silver salt alone or from silver and copper salts, are non-toxic to humans even when consumed directly in highly concentrated form.

Oligodynamic products produced in accordance with my invention have wide commercial applicability. Aqueous dispersions of oligodynamic metal produced in accordance with the invention may be used directlyto decontaminate or sterilize materials, structures and com modities of many types. Thus, food products, fruits, vegetables, drinking Water, and the like may be treated with the material by direct addition to destroy harmful living organisms initially present. The products of my invention may be employed to inhibit growth of algae and fungi in swimming pools and the like, to control slime growth in paper mills, knitting emulsions and the like, and to control bacteria in secondary oil recovery proc esses. Metal, plastic and fibrous structures of many types may be sterilized by applying thereto liquid dispersions prc pared in accordance with the invention. Thus, the material may be employed to treat containers, pieces of chemical equipment, surgical instruments, operating room equipment and the like. Fibrous structures such as sur-' gical bandages, paper, wrapping materials, textiles, and leather may be directly contacted with the products of the invention. In all such application, the oligodynamic products function initially to sterilize the structure, and the extremely small oligodynamic microparticles are adsorbed and mechanically trapped on the surfaces of the structure to provide long lasting residual biological activity.

Because of the increased eflicacy of my products and the eifect of residual biological activity, they are particularly valuable for use as a counter-measure in biological warfare. Thus, food products and articles, and utensils of every day necessity once contaminated may be treated with my products, as by a simple dipping operation, to initially sterilize the same and also to PIO- vide a lasting sterilizing effect.

I find that the products of the invention are effective as preservants for such commodities as foods, furs, leather, paper, textiles and the like. They may also be used as general disinfectants, as topical remedies for athletes foot and like afflictions, and as components for soaps, detergents, toothpastes, cosmetics, and the like.

It will be noted that a number of the foregoing applications are of primary importance because of the phenomenon, characteristic to my products, which I have referred to as residual biological activity. I have observed that this phenomenon occurs to a material extent only when the particle size of the oligodynamic product is very small. Thus, the phenomenon is manifested by, products containing oligodynamic metal particles smaller than 200 A.U., but apparently is not significantly man: ifested when the particle size is in the neighborhood of 400-1000 A.U. Further, it appears that the residual activity increases very greatly as the particle size is decreased below about 100 A.U., and is very marked when the particle size is in the range of 20-75 A.U. This relation of residual activity to particle size is apparently explainable on two grounds. First, it appears that the smaller the particle size the greater is the amount of oligodynamic metal adsorbed and trapped on the treated surface. Second, it appears that the residual activity depends upon solubility of the oligodynamic metal adhered to the treated surface, so that the effect is negligible if the particle is inordinately large, even though the particle should be held on the treated surface.

I claim:

The process of producing oligodynamic metal microbicides comprising forming an aqueous solution of a. water soluble oligodynamic metal salt containing a colloid stabilizing proportion of an ionizable-halogenwfr'ec gelatin having a viscosity of 20-40 millipoises, an i80- References Cited in the file of this patent UNITED STATES PATENTS 1,685,204 Schreier Sept. 25, 1928 15 2,132,886 Voelker Oct. 11, 1938 2,220,187 Wilmans Nov. 5, 1940 FOREIGN PATENTS France 5. June 4,1945 France Jan. 16, 1933 (Addition to No. 656,569)

OTHER REFERENCES F. E. Ross: The Physics of the Developed Photographic Image, D. Van Nostrand Co;, New York, 1924,

Baker: Photo. Emulsion Technique, 2nd ed., 1948, 513. 33-35.

Yagi: Rev. Phys. Chem., Japan, Vol.14, pp. 115-127,-

1940, through Chem. Abst., vol. 35, p. 4264. V

Gutbier et al.: Kolloid-Z, volt 30, 1922, pp. 31-35, through Chem. Abst., vol. 16, p. 1350. 

